nx_heap.nx

heap.nx -- binary min-heap (priority queue). O(log n) insert + extract-min. Used for: event scheduling (timer queues), Dijkstra's shortest path, A* search, top-K selection, garbage-collected memory tracing. Stores i64 keys with associated i64 values (use as priority + payload pointers cast to i64 for richer payloads). Invariants: H1 Min element is always at index 0. H2 For node at index i, children at 2i+1 and 2i+2; parent at (i-1)/2. Standard implicit-tree layout. H3 Insert grows when capacity would be exceeded -- realloc to 2x current. We don't realloc today (NishiLang sys_mmap is one-shot); caller picks initial cap big enough. H4 Stable for equal priorities is NOT guaranteed; insertion order may not be preserved among same-key entries.